Examples of the above-mentioned gripping device include a chuck that grips an object with jaws screwed with feed screws, and a vice that grips an object with a movable body screwed with a feed screw and a fixed body fixed to a base.
By the way, in the case where an operation in which a large load is applied to a gripped object is performed, it is necessary to increase a force gripping the object. Therefore, there has been proposed a gripping device including a mechanism for amplifying the gripping force. An example of such a gripping device is a vice disclosed in Japanese Unexamined Patent Application Publication No. 2000-117646.
This vice includes a body having guide rails formed thereon, a fixed jaw formed integrally with the body, a movable jaw arranged in a manner to be movable in directions toward and away from the fixed jaw while being guided by the guide rails, a spindle engaged with the movable jaw for moving the movable jaw forward and backward, a force increasing mechanism moving the spindle, and other components. The force increasing mechanism includes a pressing member that is moved with an amplified force generated by amplifying, by a mechanical action, a rotational force generated by driving and rotating a drive shaft with a handle or the like, and the spindle is in contact with the pressing member.
In this vice, when gripping an object, the movable jaw is moved toward the fixed jaw by rotating the spindle and the object is gripped with the movable jaw and the fixed jaw, and then the pressing member of the force increasing mechanism is moved. Thereby, the spindle is pressed by the pressing member and thereby moved and the movable jaw engaged with the spindle is further moved toward the object, whereby the force gripping the object is additionally amplified.
Further, as for a mechanism for amplifying a gripping force, there has been proposed also a configuration as shown in FIGS. 18 and 19. Note that FIGS. 18 and 19 show a part of a chuck 100 including a mechanism for amplifying a gripping force.
As shown in FIGS. 18 and 19, the chuck 100 is composed of a board shaped body 101, a gripping jaw 102 having a screw hole 102a formed therein and configured to be moved forward and backward along a guide groove formed in the body 101, a feed screw 103 screwed with the screw hole 102a of the gripping jaw 102 and having a hexagonal portion 103a formed at one end thereof, a first gear 104 having an arcuate shape and fixed to an outer peripheral surface of the body 101 to surround the one end of the feed screw 103, a crank 105 having at one end thereof a second gear 106, which meshes with the first gear 104, and a hexagonal portion 105a, to which a handle 107 mentioned below is attached, and attached at the other end thereof to the hexagonal portion 103a of the feed screw 103, the handle 107 attached to the hexagonal portion 105a, and other components.
According to this chuck 100, in a state where the crack 105 and the handle 107 are detached, the gripping jaw 102 is moved toward an object by rotating the feed screw 103 to cause the object to be gripped by the gripping jaw 102. Thereafter, the crank 105 and the handle 107 are attached and the handle 107 is rotated. Thereby, a handle torque is amplified by a factor of a predetermined reduction gear ratio and the amplified handle torque is input into the feed screw 103.
Note that the reduction gear ratio is determined by:Reduction gear ratio=Z1′/Z2′+1,  (Equation 1)wherein Z1′ is the number of teeth of the first gear and Z2′ is the number of teeth of the second gear. Based on a structural relationship, the reduction gear ratio is about 5 to 8.
Thus, in each of the above-described grapping devices, a thrust generated by the feed screw can be additionally amplified.
However, in the above-described vice, because of the configuration in which the force increasing mechanism is provided at one end side of the spindle, it is unavoidable that the overall size of the vice is increased by the force increasing mechanism. Further, the above-described chuck has a problem that, even when a stronger gripping force is desired to be applied to the object, there is a limit to the gripping force applied to the object due to structural problems.
Accordingly, the applicant of the present application has proposed a feed structure which is capable of applying a strong gripping force to an object and which allows a gripping device to have a smaller size than the conventional devices (Japanese Patent Application No. 2013-051544).
As shown in FIGS. 20 and 21, this feed structure 200 is composed of a cylindrical body 201 having a male screw portion 202 formed on an outer peripheral surface thereof and having a female screw portion 203 formed on a portion of an inner peripheral surface thereof, a first receiving body 204 having a through hole formed therein and fitted in one end side of the cylindrical body 201, a second receiving body 206 fitted in the other end side of the cylindrical body 201, an eccentric shaft 207 consisting of a base shaft portion 208 and an eccentric portion 209, the base shaft portion 208 being inserted in the through hole of the first receiving body 204, an external gear 210 having a teeth portion formed on an outer peripheral surface thereof and having a through hole bored through the center thereof, the trough hole having the eccentric portion 209 of the eccentric shaft 207 inserted therein, an internal gear 212 having a teeth portion formed on an inner peripheral surface thereof, the teeth portion partially meshing with the teeth portion of the external gear 210, and a screw body 213 having a male screw portion formed on an outer peripheral surface thereof and disposed in the cylindrical body 201 with the male screw portion thereof meshing with the female screw portion 203 of the cylindrical body 201, and with one end side thereof being engaged with the internal gear 212.
Further, the first receiving body 204 has a plurality of recesses 205 formed in a surface thereof facing the external gear 210, the recesses 205 being formed at equal intervals along a circumferential direction of the first receiving body 204. Further, the external gear 210 has protrusions 211 formed on a surface thereof facing the first receiving body 204, the protrusions 211 being formed at equal intervals along a circumferential direction of the external gear 210 and being freely fitted in the recesses 205. Note that the feed structure 200 has a configuration in which the internal gear 212 has more tooth than the external gear 210.
In this feed structure 200, for example, in a state where the feed structure 200 is rotatably supported in a predetermined posture in an appropriate chuck body and the male screw portion 202 formed on the outer peripheral surface of the cylindrical body 201 meshes with a female screw portion of an appropriate gripping jaw, the first receiving body 204 is rotated in a predetermined direction to move the gripping jaw and bring the gripping jaw into contact with an object, and then the eccentric shaft 207 is rotated in a predetermined direction. Thereby, the external gear 210 with the eccentric portion 209 of the eccentric shaft 207 being inserted therein is turned with a radius equal to eccentricity of the eccentric portion 209 around an axial center of the base shaft portion 208 and the internal gear 212 meshing with the external gear 210 is rotated in the same direction by one tooth per revolution of the eccentric shaft 207.
Note that the external gear 210 and the internal gear 212 in the feed structure 200 form a so-called hypocycloid mechanism. The reduction gear ratio in this hypocycloid mechanism is determined by:Reduction gear ratio=Z1/(Z2−Z1)+1,  (Equation 2)where Z1 is the number of teeth of the external gear 210 and Z2 is the number of teeth of the internal gear 212.
Therefore, for example, in the case where the number of teeth of the external gear 210 (Z1) is 29 and the number of teeth of the internal gear 212 (Z2) is 30, the reduction gear ratio obtained is 30, that is, a reduction gear ratio significantly improved over that of the above-described chuck 100 is obtained.
Further, when the internal gear 212 is rotated, the screw body 213 engaged with the internal gear 212 is rotated with a torque larger by a factor of a predetermined number than a torque input from the eccentric shaft 207, whereby the cylindrical body 201 whose female screw portion 203 is screwed with the male screw portion of the screw body 213 is moved with a large force. Therefore, a strong thrust can be added to the gripping force; consequently, the object can be gripped with a gripping force stronger than those of the conventional devices.
Further, because the hypocycloid mechanism as a force increasing mechanism is incorporated in the feed structure 200, the overall device size can be reduced.